I think it may have been a fault with the broadcast of Dragon's Den as I haven't noticed it since. I'll keep my eye open and try and record a sample if it pops up again.
Sorry to quote myself here but I think it may still be happening. I have a clip of Dragon's Den from last night, it's not a long clip but it does sometimes show my issues. It doesn't always though so I'm not sure what that's about. As I mentioned earlier the playback is sort of stuttery at times and sometimes shows scanlines when changing cameras, but not always, and not always at the same times when rewatching. I noticed this again earlier on a different channel but wasn't able to get a clip. The weird thing is that MediaInfo says that the file is progressive and not interlaced.
I've uploaded the clip @ Dragons'%20Den.ts It's about a minute long and 50MB.